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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
The Forces

Concepts Of Physics MCQ Edition [Volume 1] · Physics · The Forces

Calculate the ratio of the magnitude of the electric force to the...

Calculate the ratio of the magnitude of the electric force to the gravitational force exerted between two protons.

Options

  1. A1.24×10391.24 \times 10^{39}
  2. B1.24×10361.24 \times 10^{36}
  3. C1.24×10421.24 \times 10^{42}
  4. D8.06×10−378.06 \times 10^{-37}

Correct answer

B. 1.24×10361.24 \times 10^{36}

Step-by-step solution

The electric force between two protons separated by a distance rr is given by Coulomb's law:

Fe=14πϵ0e2r2F_{e} = \dfrac{1}{4\pi\epsilon_{0}} \dfrac{e^2}{r^2}

The gravitational force between them is given by Newton's law of gravitation:

Fg=Gmp2r2F_{g} = G \dfrac{m_{p}^2}{r^2}

The ratio of the electric force to the gravitational force is:

FeFg=e24πϵ0Gmp2\dfrac{F_{e}}{F_{g}} = \dfrac{e^2}{4\pi\epsilon_{0} G m_{p}^2}

Substituting the standard values:
e=1.6×10−19 Ce = 1.6 \times 10^{-19} \text{ C}
14πϵ0=9×109 N m2/C2\dfrac{1}{4\pi\epsilon_{0}} = 9 \times 10^9 \text{ N m}^2\text{/C}^2
G=6.67×10−11 N m2/kg2G = 6.67 \times 10^{-11} \text{ N m}^2\text{/kg}^2
mp=1.67×10−27 kgm_{p} = 1.67 \times 10^{-27} \text{ kg}

FeFg=9×109×(1.6×10−19)26.67×10−11×(1.67×10−27)2\dfrac{F_{e}}{F_{g}} = \dfrac{9 \times 10^9 \times (1.6 \times 10^{-19})^2}{6.67 \times 10^{-11} \times (1.67 \times 10^{-27})^2}

FeFg=9×109×2.56×10−386.67×10−11×2.7889×10−54\dfrac{F_{e}}{F_{g}} = \dfrac{9 \times 10^9 \times 2.56 \times 10^{-38}}{6.67 \times 10^{-11} \times 2.7889 \times 10^{-54}}

FeFg=23.04×10−2918.60×10−65\dfrac{F_{e}}{F_{g}} = \dfrac{23.04 \times 10^{-29}}{18.60 \times 10^{-65}}

FeFg≈1.24×1036\dfrac{F_{e}}{F_{g}} \approx 1.24 \times 10^{36}
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